In U.S. Pat. Nos. 5,844,086 and 6,005,076 (“Murray II”), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for the isolation of protein isolates from oil seed meal having a significant fat content, including canola oil seed meal having such content. The steps involved in this process include solubilizing proteinaceous material from oil seed meal, which also solubilizes fat in the meal and removing fat from the resulting aqueous protein solution. The aqueous protein solution may be separated from the residual oil seed meal before or after the fat removal step. The defatted protein solution then is concentrated to increase the protein concentration while maintaining the ionic strength substantially constant, after which the concentrated protein solution may be subjected to a further fat removal step. The concentrated protein solution then is diluted to cause the formation of a cloud-like mass of highly aggregated protein molecules as discrete protein droplets in micellar form. The protein micelles are allowed to settle to form an aggregated, coalesced, dense amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from residual aqueous phase and dried.
The protein isolate has a protein content (as determined by Kjeldahl Nx 6.25) of at least about 90 wt %, is substantially undenatured (as determined by differential scanning calorimetry) and has a low residual fat content of less than about 1 wt %. The yield of protein isolate obtained using this procedure, in terms of the proportion of protein extracted from the oil seed meal which is recovered as dried protein isolate was generally less than 40 wt %, typically around 20 wt %.
The procedure described in the aforementioned patents was developed as a modification to and improvement on the procedure for forming a protein isolate from a variety of protein source materials, including oil seeds, as described in U.S. Pat. No. 4,208,323 (Murray IB). The oil seed meals available in 1980, when U.S. Pat. No. 4,208,323 issued, did not have the fat contamination levels of canola oil seed meals available at the time of the Murray II patents, and, as a consequence, the procedure of U.S. Pat. No. 4,208,323 cannot produce from oil seed meals processed according to the Murray II process, proteinaceous materials which have more than 90 wt % protein content. There is no description of any specific experiments in U.S. Pat. No. 4,208,323 carried out using rapeseed (canola) meal as the starting material.
U.S. Pat. No. 4,208,323 itself was designed to be an improvement on the process described in U.S. Pat. Nos. 4,169,090 and 4,285,862 (Murray IA) by the introduction of the concentration step prior to dilution to form the PMM. The latter step served to improve the yield of protein isolate from around 20 wt % for the Murray IA process.
In copending U.S. Patent Applications Ser. No. 60/288,415 filed May 4, 2001, Ser. No. 60/326,987 filed Oct. 5, 2001, Ser. No. 60/331,066 filed Nov. 7, 2001, Ser. No. 60/333,494 filed Nov. 28, 2001, Ser. No. 60/374,801 filed Apr. 24, 2002 and Ser. No. 10/137,391 filed May 3, 2002, assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there are described further improvements on these prior art protein isolation procedures as they apply to oil seeds to obtain improved yields of dried product protein isolate in terms of the proportion of the protein extracted from the oil seeds which is recovered as protein isolate and to obtain protein isolate of high purity, usually at least about 100 wt % at a Kjeldahl nitrogen (N) conversion rate of Nx 6.25. The procedure is employed particularly to produce a canola protein isolate.
In the procedure described in the aforementioned US Patent Applications, the oil seed meal is extracted with an aqueous food grade salt solution. The resulting protein extract solution, after an initial treatment with pigment adsorbing agent, if desired, is reduced in volume using ultrafiltration membranes to provide a concentrated protein solution having a protein content in excess of about 200 g/L. The concentrated protein solution then is diluted into chilled water having a temperature below about 15° C., resulting in the formation of a white cloud of protein micelles which are allowed to separate. Following removal of the supernatant, the precipitated, viscous sticky mass (PMM) is dried.
In one embodiment of the process described in the aforementioned U.S. Patent Application Ser. No. 60/288,415 as it is applied to canola protein isolate and as described in copending U.S. Patent Applications Ser. Nos. 60/326,987, 60/331,066 60/333,494, 60/374,801 and 10/137,391, the supernatant from the PMM settling step is processed to recover a protein isolate comprising dried protein from the wet PMM and supernatant. This may be effected by initially concentrating the supernatant using ultrafiltration membranes, mixing the concentrated supernatant with the wet PMM and drying the mixture. The resulting canola protein isolate has a high purity of at least about 90 wt % protein, preferably at least about 100 wt %, at a Kjeldahl conversion rate Nx 6.25. This latter product is termed “Puratein” by the applicants.
In copending U.S. Patent Applications Ser. No. 60/331,646 filed Nov. 20, 2001 and Ser. No. 60/383,809 filed May 30, 2002, assigned to the assignee hereof and the disclosure of which are incorporated herein by reference, there is described a continuous process for making canola protein isolates. In accordance therewith, canola oil seed meal is continuously mixed with a food grade salt solution, the mixture is conveyed through a pipe while extracting protein from the canola oil seed meal to form an aqueous protein solution, the aqueous protein solution is continuously separated from residual canola oil seed meal, the aqueous protein solution is continuously conveyed through a selective membrane operation to increase the protein content of the aqueous protein solution to at least about 200 g/L while maintaining the ionic strength substantially constant, the resulting concentrated protein solution is continuously mixed with chilled water to cause the formation of protein micelles, and the protein micelles are continuously permitted to settle while the supernatant is continuously overflowed until the desired amount of protein micellar mass has accumulated in the settling vessel. The protein micellar mass is removed from the settling vessel and may be dried. The protein micellar mass has a protein content of at least about 100 wt % as determined by Kjeldahl nitrogen (Nx 6.25). As in the case of the aforementioned pending United States patent applications, the overflowed supernatant may be proceeded to recover a protein isolate comprising dried protein from the wet PMM and supernatant. This procedure also may be effected on a semi-continuous basis.
As described in copending U.S. Application Ser. No. 60/332,165 filed Apr. 15, 2002, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, the settled PMM and protein derived from the supernatant have different relative proportions of the 12S, 7S and 2S proteins of canola protein. The PMM derived protein isolate, having a protein content of at least about 90 wt %, preferably at least about 100 wt %, has a protein component content of about 60 to about 98 wt % of 7S protein, about 1 to about 15 wt % of 12S protein and 0 to about 25 wt % of 2S protein. The supernatant-derived canola protein isolate having a protein content of at least about 90 wt %, preferably at least about 100 wt %, has a protein component content of 0 to about 5 wt % of 12S protein, about 5 to about 40 wt % of 7S protein and about 60 to about 95 wt % of 2S protein.
The processing of the supernatant from the PMM settling step to remove a protein isolate comprising dried protein from the wet PMM and supernatant then is a blend of the isolates derived from the respective sources and exhibits a composite protein component content.
Canola is also termed rapeseed or oil seed rape.